1. Field of the Invention
The present invention relates to mobile communications and, more particularly, to achieving point-to-point protocol (PPP) mobility utilizing a Mobile Internet Protocol (IP) infrastructure.
2. Description of the Related Art
In computer-related networking or telecommunications, the point-to-point protocol is used for communicating information between a source and a destination. PPP is widely used for transmitting Transmission Control Protocol/Internet protocol (TCP/IP) packets over dial-up telephone connections, such as between a general purpose computer and an Internet Service Provider (ISP). TCP/IP is a set of protocols developed by the United States Department of Defense for communications over interconnected, sometimes dissimilar, networks and has become the de facto standard for data communications over various networks, including the Internet. The point-to-point protocol (PPP) provides a standard methodology for transporting multi-protocol datagrams of information over point-to-point links. PPP comprises three main components: (1) a methodology for encapsulating multi-protocol datagrams, (2) a link control protocol (LCP) for establishing, configuring and testing the data link connection, and (3) a family of network control protocols (NCPs) for establishing and configuring different network-layer protocols.
An end-user sets up a PPP session between the source, e.g., a general purpose computer or telecommunication device, and a destination (which can also be a general purpose computer or telecommunication device) for transmitting data or information thereto. In a PPP session, once the initial negotiation phases are successfully completed, a session identifier is associated with the connection, thereby identifying the PPP session. Typically, a single PPP connection exists between an end user's computer and the destination, e.g., an Internet service provider (ISP) or another computer connected to the Internet. The PPP session is closed when the end-user of the network system completes the data or information transfer.
A PPP (point-to-point protocol) packet or frame consists of the user data and any headers of other protocols being encapsulated by the PPP. The frame is also provided with a PPP header. The PPP header contains the information necessary to identify and maintain an associated PPP session.
Encapsulation in PPP treats a collection of structured information as a whole without affecting or taking notice of its internal structure. Thus, a message or packet constructed according to one protocol (such as a TCP/IP packet) may be taken with its formatting data as an undifferentiated stream of bits that is then broken up and packaged according to the higher level point-to-point protocol to be sent over a particular network.
FIG. 1 is a diagram that generally illustrates an exemplary point-to-point communication network over the Public Switched Telephone Network (PSTN). The PSTN is the international telephone system based on copper wires carrying analog voice data. An end-user at his or her personal computer (PC 10), which is the source, commands a software program at PC 10, e.g., MICROSOFT DIAL-UP NETWORKING™, to utilize a modem 11 to connect PC 10 to the ISP's modem server 20 via the PSTN and the ISP's modem 21. Upon connection, a PPP session is established and the user data, in the form of IP packets encapsulated in accordance with PPP, are transmitted to the ISP's modem 21 and its server 20. The server 20 may be the final destination and it may use the information. Alternatively, server 20 may forward the data to its final destination (e.g., a computer at a designated IP address on the Internet).
Layer 2 Tunneling Protocol (L2TP) was developed to enable a PPP session to be established over the Internet, instead of strictly over the PSTN. An L2TP system requires an L2TP access concentrator (LAC), which is a device attached to a switched network system, e.g., the PSTN or the integrated services digital network (ISDN) or co-located with a PPP end system capable of handling the L2TP. The LAC is the initiator of incoming calls to a network and the receiver of outgoing calls therefrom. It encapsulates the PPP data packets.
The L2TP system also requires a L2TP network server (LNS) which unencapsulates the packets, revealing the original PPP frames. An LNS handles the server side of the L2TP connection by acting as the receiver of L2TP tunnel requests from the LAC and terminating the PPP sessions from the end user. The LNS is capable of PPP session termination.
A tunnel is a technology that enables one network to send its data over another network's connections. Tunneling works by encapsulating a network protocol within packets carried by the second network. For example, L2TP technology enables the use of the Internet to extend a PPP link to a point or entity that is not on a directly connected network. This is accomplished by embedding its own network protocol within the TCP/IP packets carried by the Internet.
FIG. 2 illustrates a way of expanding the use of PPP across the Internet, so that it does not rely exclusively on transmission by way of the PSTN. As shown in FIG. 2, PC 10 is caused to dial over the PSTN into a modem 13 at a local Point of Presence (PoP) 14, which is a device accessible with a local phone call by the end-user and which is connected to a data network (e.g. the Internet). PC 10 then runs PPP to establish a connection to the PoP 14. At this point, an L2TP Access Concentrator (LAC) 15 located within the PoP encapsulates the PPP frames into IP packets according to the L2TP protocol and transmits them over the Internet to the L2TP Network Server (LNS) 23 on the destination network.
The LNS 23 unencapsulates the L2TP packets which reveals the PPP frames. Acting as a PPP termination point, the LNS unencapulates the PPP frames which reveals the original IP packets. It then forwards the data to its intended destination, e.g. server 20. Unencapsulation is essentially the stripping off of the outer header of a PPP packet, thereby revealing the content of the rest of the packet. This approach enables an end-user of the network system to make a local telephone call to connect to a destination that could be very far away, and which is more easily reached over the Internet.
FIG. 3 is a diagram illustrating a wireless communication network that replaces the modem 11 (described in conjunction with FIG. 2) with wireless customer premises equipment (CPE) that includes a L2TP Access Concentrator (CPE/LAC) 101, and places an L2TP Access Concentrator (LAC) 16, 18 at each of the base stations 17, 19 in the wireless system. Customer premise equipment is typically the equipment located at the customer's site which denotes the demarcation point between the customer (or end user) and the service provider, e.g., a T1 line, wireless modem , radio, cable modem, digital subscriber line (DSL) or asymmetric digital subscriber line (ADSL) modems.
For example, the end-user initiates a PPP session from PC 10 to the LAC 18 at base station 19 via the radio tower 19A. LAC 18 creates an L2TP tunnel over the Internet to LNS 23. All PPP frames sent from PC 10 to LAC 18 are encapsulated in L2TP packets and sent to the LNS 23, which unencapsulates the L2TP packets and reveals the PPP frames. The LNS 23 also terminates the PPP connection, revealing the original IP packets and forwards them to their intended destination, i.e. server 20.
As PC 10 moves from the transmitting range of the base station 19 to that of the base station, 17 the new base station 17 has no knowledge of the previous PPP connection to the LNS 23. LAC 16 at the base station 17, with a different IP address, cannot take over an existing L2TP/PPP session for transmitting the information. In order for the base station 17 to service the mobile end-user as PC 10 moves to become PC 10′ (and CPE/LAC 101 becomes CPE/LAC 101′) in the transmitting range of base station 17, a new PPP session must be initiated by the end-user to LAC 16 associated with the base station 17 via the radio tower 17A.
In each of the above approaches, if the end-user moves from one location to another, the end-user must disconnect from the Internet service provider and re-establish a new PPP session from the new location. This puts the end-user at a disadvantage, as repeated reconnection can be cumbersome and economically inefficient to execute. In particular, if the end-user is mobile and a reconnection is required, the transmission of information is interrupted which is not cost effective and, furthermore, may lead to loss of important information.
Therefore, there is a general need in the art for an improved method and system for communicating information between a source and a destination using PPP. In particular, there is a need in the art for a method and system for communicating PPP packets between a source and a destination without the need for reconnection if the source is mobile.